An internal combustion engine burns a mixture of fuel and oxidizer in a combustion chamber to create high temperature and pressure gases that expand to provide useful work. Some engines may use valves to control intake of oxidizer and sometimes fuel as well as to control exhaust gases. These engines conventionally use mechanically driven camshafts to actuate the valves and control combustion by the timing, duration and sometimes lift of the valves, thus controlling the intake and exhaust of air, fuel and exhaust gases.
Unfortunately, conventional mechanically driven camshafts provide the same timing, duration and lift of the valves under all engine operating conditions. For example, a camshaft may be designed to improve low engine speed torque but this also affects high engine speed horsepower, overall engine efficiency, exhaust emissions and noise, vibration and harshness (NVH). Due to these factors, variable valve timing cam driven systems have been designed to vary aspects of valve timing, duration, or lift based on engine operating speed. While these systems allow increased control over pumping losses, combustion parameters, volumetric efficiency, etc., these systems still provide sliding friction losses, typically only operate on a bank of cylinders and therefore do not individually control cylinders, and decrease overall efficiency by having to overcome valve spring forces.
Electromagnetic/electronic valve actuation (EVA) engines have been developed that use electromagnetic solenoid actuators to open and close valves, providing variable valve control without some of the detriments of cam operated variable valve systems. Valve timing may be computed based on intake and exhaust manifold pressures, air charge estimation, fuel charge estimation, driver demand, etc. EVA control allows for dynamic changes to valve timing based on calculations of these variables. One such electronically controlled variable valve timing system has been disclosed in U.S. Pat. No. 6,502,543, issued to Arai, et al.
In Arai, an intake-air quantity control apparatus advances intake valve closure timing if an intake-air quantity is above a threshold value, and adjusts a throttle opening if an intake-air quantity is below a threshold value, in order to adjust an actual intake-air quantity closer to a desired value. However, Arai uses a single control unit to receive measurements of engine operating conditions, calculate valve timing, and adjust a throttle opening with a throttle actuator. Use of one control unit may disrupt the response of the control unit to other functions and thus requires a lead time to calculate valve timing well in advance of actual valve open and close events.
In one approach, as described in U.S. Pat. No. 6,866,012 issued to Hayase, et al., a multiple control unit approach to distribute processing power for an EVA engine is described. In particular, Hayase provides a method and apparatus to assign a controller to a group of valves with non-overlapping opening periods while the internal combustion engine is operated in a low speed low load region to reduce operation noise. Additionally, Hayase provides dividing electromagnetically driven valves in an internal combustion engine into plural valve groups to minimize overlap of concentrated control periods for the valves, and controlling the valves in each of the valve groups using a single control body.
However, the inventors herein have recognized disadvantages with this approach. Specifically, when valve timing is initially computed in a master controller and sent to slave controllers, computation and transmission delays allow engine operating conditions such as manifold pressures, in-cylinder pressure, driver demands, etc., to change considerably by the time the valve timing information is used at a valve controller. Conversely, if the valve timing information is too up to date, it will not reach the valve controller within a meaningful time to allow actuation before the corresponding cylinder combustion event. A conventional approach provides valve timing updates every 900 degrees of crank rotation in order to not be too late to be relevant or too early to be calculated. However, in such a degree based delay approach, timing information is fast at a slow engine speed and slow at a fast engine speed.
The inventors herein have recognized the above-mentioned disadvantages and have developed a system that improves communication and data exchange between a valve controller and an engine controller.